I have a betta who is a Petsmart rescue and is doing lovely in his 'less than a gallon' bowl.. I think he's really cramped though and needs a new home so I am thinking about this sort of setup to purchase tommorow:

WARNING: Plastic plants, in many cases, will tear your bettas fins up. Bettas like to lean up against stuff and rest and hide under leaves, thus their fins often get caught on the sharp plastic edges.
Do your fish a favor and get him good silk plants, that or real ones. Take it from me, I work at a fish store, and all those people who buy cheap plastic plants for their Bettas eventually come back complaining about their Betta's fins getting all torn up. Just sayin...